INTEGRATIVE LEVELS 



The question had always been particularly serious for those bio- 

 chemists who interested themselves in the problems of morphology. 

 The enzymes involved in metabolism may be isolated and studied in 

 relatively simple systems, analyses may be made of the substances 

 entering and leaving the living body, even the blood and tissue fluids 

 may be examined in relation to every conceivable bodily activity, 

 change or disease — but all this avoids the main problem of biology, 

 the origin, nature, and maintenance of specific organic structure. 

 The building of a bridge between biochemical and morphological 

 concepts is perhaps the most important task before biologists at the 

 present time, and it may well be long before it is satisfactorily accom- 

 plished. But in the course of the present century several branches of 

 study of great value in this connection have sprung up, particularly 

 in embryology, where the changing organic form is the most obvious 

 variable during development. Experimental and chemical embryology'- 

 together have made much progress towards the unification of chemical 

 and morphological concepts. But this impressive change of morpho- 

 logical form takes place along the time-axis, and just as we have seen 

 that in the far-away realm of the history of theology, the conviction 

 of the importance of time was brought home to your lecturer, so also 

 it was inescapable in the realm of biological science. In the develop- 

 ment of the individual organism, as in that of organisms in general, 

 progression took place from low to high complexity, from inferior 



^ It is interesting that Spencer himself had something to say on chemical embryology, 

 in his time an almost uncharted field : 



"The clearest, most numerous, and most varied illustrations of the advance in 

 multiformity that accompanies the advance in integration, are furnished by living 

 bodies. . . . The history of every plant and every animal, while it is a history of 

 increasing bulk, is also a history of simultaneously-increasing differences among 

 the parts. This transformation has several aspects. The chemical composition, 

 which is almost uniform throughout the substance of a germ, vegetal or animal, 

 gradually ceases to be uniform. The several compounds, nitrogenous and non- 

 nitrogenous, which v-'ere homogeneously mixed, segregate by degrees, become 

 diversely proportioned in diverse places, and produce new compounds by trans- 

 formation or modification. . . . The yelk, or essential part of an animal-ovum, 

 having components which are at first evenly diffused among one another, chemically 

 transforms itself in like manner. Its proteid, its fats, its salts, become dissimilarly 

 proportioned in different localities; and multiplication of isomeric forms leads to 

 further mixtures and combinations that constitute minor distinctions of parts. Here 

 a mass, darkening by accumulation of haematine, presently dissolves into blood. 

 There fatty and albuminous matters uniting, compose nerve-tissue. At this spot 

 the nitrogenous substance takes on the character of cartilage; at that calcareous 

 salts, gathering togetlier in the cartilage, lay the foundation of bone. All these 

 chemical differentiations slowly become more marked and more numerous." 

 FP, p. 306. 



245 



